1. Technical Field
The present invention relates in general to an improved hard disk drive design and, in particular, to an improved design for a hard disk drive having a motor bracket shroud that completely encircles the outside diameter of the motor hub flange in a hard disk drive.
2. Description of the Related Art
Generally, a data access and storage system consists of one or more storage devices that store data on magnetic or optical storage media. For example, a magnetic storage device is known as a direct access storage device (DASD) or a hard disk drive (HDD) and includes one or more disks and a disk controller to manage local operations concerning the disks. The hard disks themselves are usually made of aluminum alloy or a mixture of glass and ceramic, and are covered with a magnetic coating. Typically, one to six disks are stacked vertically on a common spindle that is turned by a disk drive motor at several thousand revolutions per minute (rpm).
A typical HDD also utilizes an actuator assembly. The actuator moves magnetic read/write heads to the desired location on the rotating disk so as to write information to or read data from that location. Within most HDDs, the magnetic read/write head is mounted on a slider. A slider generally serves to mechanically support the head and any electrical connections between the head and the rest of the disk drive system. The slider is aerodynamically shaped to glide over moving air in order to maintain a uniform distance from the surface of the rotating disk, thereby preventing the head from undesirably contacting the disk.
Typically, a slider is formed with an aerodynamic pattern of protrusions on its air bearing surface (ABS) that enables the slider to fly at a constant height close to the disk during operation of the disk drive. A slider is associated with each side of each disk and flies just over the disk's surface. Each slider is mounted on a suspension to form a head gimbal assembly (HGA). The HGA is then attached to a semi-rigid actuator arm that supports the entire head flying unit. Several semi-rigid arms may be combined to form a single movable unit having either a linear bearing or a rotary pivotal bearing system.
The head and arm assembly is linearly or pivotally moved utilizing a magnet/coil structure that is often called a voice coil motor (VCM). The stator of a VCM is mounted to a base plate or casting on which the spindle is also mounted. The base casting with its spindle, actuator VCM, and internal filtration system is then enclosed with a cover and seal assembly to ensure that no contaminants can enter and adversely affect the reliability of the slider flying over the disk. When current is fed to the motor, the VCM develops force or torque that is substantially proportional to the applied current. The arm acceleration is therefore substantially proportional to the magnitude of the current. As the read/write head approaches a desired track, a reverse polarity signal is applied to the actuator, causing the signal to act as a brake, and ideally causing the read/write head to stop and settle directly over the desired track.
One example of a prior art spindle motor 11 for a disk drive is shown in FIG. 1. Motor 11 has a stationary motor bracket 13 and a hub 15 that rotates relative to the bracket 13. The hub 15 has a flange 17 that rotates with the hub 15 at very high rotational speeds (e.g., 10,000 to 15,000 rpm). There is a small radial gap 19 located between bracket 13 and flange 17 to allow rotation. Bracket 13 is also provided with a generally rectangular notch 21 that extends all the way from the outer diameter of the bracket 13 to the radial gap 19, as shown. The notch 21 exposes the outer diameter radial edge 23 of the flange 17. The notch 21 is needed in bracket 13 in order to accommodate a pivot actuator (not shown). The additional space provided by notch 21 is especially critical for high disk count disk drives, which must fit within the same form factor as smaller disk count disk drives.
Unfortunately, the exposure of the outer diameter radial edge 23 of flange 17 abruptly disturbs the flow of air during rotation of the hub 15. The edges of the notch 21 are discontinuous with respect to the bracket 13 as they form a “step” having an axial height differential relative to the flange 17 and edge 23. Thus, the required presence of notch 21 causes air flow disturbances that are generated by the rotating motor hub flange 17. Air flow disturbance, especially when near the actuator arms or head suspensions, can impact track misregistration (TMR). In addition, the notch 21 increases the probability of circulating contamination particles inside the motor 11 out to the disk drive due to the irregular air flow patterns, thereby impeding the performance of the disk drive. Thus, an improved design for attenuating such air flow disturbances thereof would be desirable.